Light emitting devices such as light emitting diodes (LEDs) based on group III-V nitride semiconductors such as gallium nitride (GaN) have been put into practice.
Since wide GaN substrate cannot be produced, the LEDs have been produced on a heteroepitaxial substrate such as sapphire. The use of sapphire substrate is problematic due to lattice mismatch and thermal expansion mismatch between GaN and the sapphire substrate. One consequence of thermal expansion mismatch is bowing of the GaN/sapphire substrate structure, which leads to cracking and difficulty in fabricating devices with small feature sizes. A solution for this is to form a plurality of grooves on the surface of the sapphire substrate by lithography or etching before growing the GaN layer. However, the process of lithography and etching is complex, high in cost, and will pollute the sapphire substrate.
What is needed, therefore, is to provide a method for solving the problem discussed above.